Taking the popular herb ginseng may undermine the blood-thinning action of the prescription drug warfarin (Coumadin). That's the conclusion of a recent four-week study conducted at the Tang Center for Herbal Medicine Research at the University of Chicago.

Surprising Results. Of the 20 healthy men and women in the study, half were given warfarin for three days before and three days after they were given ginseng. The other half took a placebo. The results? The blood-thinning effect of warfarin was significantly reduced in the ginseng group compared to the placebo group.

Ginsenosides, the active compounds in ginseng, may speed up enzymes in the liver that break down warfarin, suggest the researchers. But ginseng is also known to act as a blood thinner at times. So, it may be hard to know how it will behave in your body.

What to Do. EN's advice? Be sure to tell your physician if you are taking ginseng, as well as any other herbal remedies.